#include<iostream>
using namespace std;
int main(){
    int arr[35];
    int n;
    arr[1]=1;
    arr[2]=2;
    for(int i=3;i<35;i++){
        arr[i]=arr[i-1]+arr[i-2];
    }
    cin>>n;
    cout<<arr[n]<<endl;
    return 0;
}
